1. Field of the Invention
This invention relates to a manufacturing method of a piston for an internal combustion engine wherein a circumference of a top ring groove is complex-reinforced by an inorganic fiber assembly and wherein an oil cooling gallery is formed by a soluble core.
2. Description of Related Art
In a conventional method of a piston, for example in Japanese Patent Laid Open Publication No. 60-166158, a circumference of a top ring groove is reinforced by an inorganic fiber assembly or a porous metal, and an oil cooling gallery is formed near the top ring groove by using a soluble core.
The lower part of the soluble core has pinholes and the upper part of the punch mold has three poles. A pin is formed at the top of the pole and inserted in the pinhole of the soluble core.
In this condition, the soluble core is held in the punch mold and inserted in the casting mold. By the casting, the soluble core melts, and therefore the oil-cooling gallery is formed. The inorganic fiber assembly is, however, fragile and is sometimes broken in the casting, and X-ray inspection is necessary. The porous metal is expensive.